Alcohol production by hydration of olefins has conventionally been carried out by a process of using an acid catalyst such as sulfuric acid and the like. In the process of using sulfuric acid, an olefin is allowed to react with water in the presence of sulfuric acid to generate a sulfuric ester and then it hydrolyzes to generate a crude alcohol. A purified alcohol is prepared by separating an unreacted olefin, water and byproducts from the crude alcohol with rectification or other methods. In the production method, sulfuric acid necessary for the production of the sulfuric ester is in an amount equimolar with olefin, namely in terms of weight, of 70%. Therefore, because a large amount of sulfuric acid having high corrosive properties is present inside a reactor, this process has serious problems such that troubles caused by corrosion of materials in each place are easily induced in the equipment preservation aspect and an operator has a danger of receiving sulfuric acid spurted in the safety aspect.
After the hydrolysis, the separated aqueous sulfuric acid solution is again concentrated into an aqueous solution of high concentration and then submitted to recycling. The increase of the number of steps necessary for the recycling increases the cost of plant construction and the cost of heating necessary for the concentration so that the process is uneconomical. We must consider apparatus corrosion in not only reactors but also steps where sulfuric acid having a high concentration is passed through in the same manner so that the provision for corrosion results in an increase of the maintenance cost. The waste liquid containing sulfuric acid in a high concentration constantly exhausted is necessary to be neutralized with sodium hydroxide etc and a resultant sulfate is necessary to be treated as an industrial waste to increase the environmental load.
Under the circumstances, a gas phase reaction process of directly hydrating olefin and water with a phosphoric acid supported catalyst has been developed as referred to Patent literatures 1 to 3. In this process, from crude alcohol generated from the direct hydration, an unreacted olefin, water and byproducts are separated by rectification and other methods and thereby purified alcohol is prepared. This process has been industrially conducted in many cases because the steps are simplified as compared with the process of using sulfuric acid and this process has no danger of using a strong acid having a high concentration. However, in general, this process has a low conversion rate of olefin so that the production amount of alcohol per volume is very low and thereby a reactor becomes too large and also the energy required for recycle of an unreacted olefin becomes large. Further, there is a problem such that the catalyst capabilities of phosphoric acid used as a catalyst component are lowered by scattering thereof with the progress of the reaction and thereby the productivity is lowered.
As another process of the direct hydration, a process of using a water-soluble heteropolyacid as a catalyst has been developed as referred to Patent literatures 4 to 6.
In this process, an olefin and water are directly subjected to hydration in the presence of a heteropolyacid to generate crude alcohol. From the crude alcohol, unreacted olefins, heteropolyacid, water and byproducts are separated by rectification and other methods and thereby purified alcohol is prepared. Because heteropolyacid has low corrosive properties, the maintenance cost for apparatus is improved, but the concentration of heteropolyacid in the reaction steps is several thousands ppm per the flow rate of a reaction liquid and it is none too low, to make the economical properties worse. Further, no small amount of heteropolyacid is constantly discharged and thereby neutralization treatment is necessary. Similar to the sulfuric acid process, the heteropolyacid waste liquid constantly discharged is necessary to be subjected to neutralization treatment and a salt of heteropolyacid generated after the neutralization treatment is necessary to be treated as an industrial waste to increase the environmental load. Meanwhile, because heteropolyacid is expensive, it is considered that heteropolyacid is separated from the waste liquid and submitted to reuse. In this case, the cost for the separation, such as ion exchange resin treatment step and the like is large to increase the production cost. Additionally, the molar ratio of water to olefin in the raw materials is 27 and it is higher as compared with other prior techniques so that the production efficiency is lowered.
Processes of using such a soluble catalyst other than the heteropolyacid have been developed. For example, there are a process of using trifluoromethane sulfonic acid (as referred to Patent literature 7) and a process of using a titanium sulfate aqueous solution (as referred to Patent literature 8).
In any processes, however, the catalyst in a reactor inevitably has a high concentration in order to promote the reaction and thereby the production cost is increased. Further, the post treatment steps after the use of the catalyst are increased so that the plant cost is also increased in the processes.
As another direct hydration process, a process of using a strong acid ion exchange resin catalyst is also developed as referred to Patent literatures 9 to 11. In this process, an olefin and water are directly subjected to hydration reaction in a reactor filled with a solid catalyst to generate crude alcohol. From the crude alcohol, an unreacted olefin, water and byproducts are separated by rectification and other methods and thereby purified alcohol is produced. When the process of using the soluble catalyst such as sulfuric acid or heteropolyacid is employed, it is necessary to employ a step of recovering the catalyst. However, using the solid catalyst, it is unnecessary to employ the step of recovering the catalyst and also unnecessary to employ neutralization treatment of acid components contained in a waste liquid. But, in the process of using the solid catalyst, the catalyst is deteriorated with time and it is necessary to increase the temperature or decrease the production in order to keep a space time yield. For these reasons, the operation control is complicated to affect a bad influence on economic properties simultaneously. Further, the deteriorated catalyst has to be regenerated to deteriorate the economic properties in this stage. When the catalyst cannot be regenerated, exchange operation is required and thereby the catalyst exchange requires considerable several days to lower the production. Furthermore, large amounts of catalyst wastes generated are inevitably treated as an industrial waste.
In addition to the above processes, many processes of using a solid acid catalyst have been developed. For example, a process of using ZSM-5 zeolite as a catalyst is disclosed as referred to Patent literature 12. Furthermore, as a process of improving the lifetime of the solid acid catalyst or improving the capabilities thereof, some processes are disclosed as referred to Patent literatures 13 to 15. However, in any processes, the deterioration of the solid acid catalyst with time is inevitable and the fundamental improvement for the processes is necessary.
As described above, on present showing, these conventional processes have inevitable problems including economical deterioration caused by various reasons, industrial waste treatment and the like.
Previously, the present inventors invented a direct hydration process without need of an acid catalyst in the production of alcohols by hydration reaction of an olefin and water as referred to Patent literature 16. This process utilizes an acid catalyst function, which is expressed near the critical point of water.
Utilizing the technique, we have studied earnestly in order to further improve the productivity. Thus, the present invention has been accomplished.    Patent literature 1: JP-B-51(1976)-44915    Patent literature 2: JP-A-52(1977)-133095    Patent literature 3: JP-A-53(1978)-84906    Patent literature 4: JP-A-47(1972)-30608    Patent literature 5: JP-A-47(1972)-31908    Patent literature 6: JP-A-47(1972)-31909    Patent literature 7: JP-A-52(1977)-133910    Patent literature 8: JP-A-52(1977)-113904    Patent literature 9: JP-A-49(1974)-117412    Patent literature 10: JP-A-49(1974)-126607    Patent literature 11: JP-A-49(1974)-126609    Patent literature 12: JP-A-63(1988)-218251    Patent literature 13: JP-A-8(1996)-143493    Patent literature 14: JP-A-8(1996)-151339    Patent literature 15: JP-A-11(1999)-76836    Patent literature 16: JP-A-2003-34657